It has been shown that structure of glomeruli in lupus erythematosus has prognostic value. Renal morphology will be correlated with serial evaluation of anti-DNA antibodies and complement in the serum. Some 20 renal biopsies are already available for that purpose. The damage to podocytes and basement membranes will be evaluated on the ultrastructural level in cases of nephrotic syndrome associated with focal glomerular sclerosis. This damage apparently occurs in the more severe cases with poor prognosis. It has been shown that large doses of radiation affect all structural components of the kidney in the rat. For comparison purposes, smaller doses will be employed (400-2,000 rads) to determine the relative sensitivity of glomeruli, tubules and blood vessels. A correlative study will be undertaken of the early phase of aminonucleoside nephrosis (1 to 10 days), comparing the chemical composition and the ultrastructural appearance of the glomerular capillary wall and the degree of proteinuria. Pleural and peritoneal mesotheliomas in man and in experimental animals will be studied by histochemical and ultrastructural methods in order to determine the characteristic features of the cells and the nature of their secretion. The latter consists mainly of acid muco-substances including hyaluronic acid and probably other mucopolysaccharides.